The invention relates to a pump for a high-pressure cleaning appliance for delivering a cleaning liquid, comprising a pump housing in which is arranged at least one pump chamber into which at least one piston which is movable back and forth plunges, and which is connected via at least one inlet valve to a suction line and via at least one outlet valve to a pressure line, and comprising a bypass line which leads from the pressure line to the suction line, and in which is arranged an overflow valve, the valve body of which is connected to a control element which in dependence upon the flow rate of the cleaning liquid in the pressure line displaces the valve body to a closed position or an open position.
Such pumps are known from DE 93 01 796 U1. They can be used to subject a cleaning liquid, for example, water to pressure and to then direct it at an object, for example, via a pressure hose connectable to the pressure line and a nozzle head arranged at the free end of the pressure hose. In order that continued operation of the pump, with the nozzle head closed, will not lead to a continuing high pressure in the pressure line, resulting in considerable power consumption of the pump and substantial heat losses, the cleaning liquid conveyed by the pump is usually recirculated with as low a flow resistance as possible, i.e., it is fed back from the pressure line to the suction line again. For this purpose, the pressure line is connected to the suction line by a bypass line, and an overflow valve is arranged in the bypass line. During working operation of the pump, i.e., when the nozzle head is open, the overflow valve closes the flow connection between the pressure line and the suction line. During circuit operation, i.e., when the nozzle head is closed, the overflow valve opens the flow connection between the pressure line and the suction line. The overflow valve comprises a valve body, which is connected to a control element. In dependence upon the flow rate of the cleaning liquid in the pressure line, the control element displaces the valve body to a closed position or an open position. The flow rate of the cleaning liquid in the pressure line depends on whether the nozzle head is open or closed. If the nozzle head is closed, the flow rate drops, and this causes the control element to displace the valve body of the overflow valve to its open position, with the result that the pump then transfers to circuit operation. If the nozzle head is opened, the flow rate in the pressure line rises and this causes the control element to displace the valve body of the overflow valve to the closed position, with the result that the pump transfers to working operation.
In order that such pumps will have as low a weight as possible for easier handling, a compact structural size is chosen for the pumps. However, this leads to cramped space conditions in the pump housing. The provision of the individual lines and spaces for accommodating valves therefore often proves difficult in terms of manufacture and involves considerable costs.
The object of the present invention is to further develop a pump of the kind mentioned at the outset so that it can be produced at lower cost and more easily in terms of manufacturing technology.